1. Field of the Invention
The present invention relates to a valve timing control apparatus which is adapted to control the valve timing of at least one of a suction valve and an exhaust valve of an internal combustion engine according to operational conditions thereof.
2. Description of Related Art
A conventional vane type valve timing control apparatus includes a cam shaft that is driven through a timing gear or chain sprocket, and that rotates synchronously with a crank shaft of the engine. The apparatus thereby controls the valve timing of at least one of a suction valve and exhaust valve by the phase difference, due to a relative rotation, between the timing gear and the chain sprocket. Such an apparatus is disclosed in U.K. Patent Application Laid-Open Publication No. 2302391.
In this vane type of valve timing control apparatus there is, for example, a lock member that is reciprocatingly accommodated in a vane rotor constituting a cam shaft side rotating body. The lock member is fitted into a hole provided in a housing constituting a crank shaft side rotating body, thereby constraining the relative rotation between the cam shaft side rotating body and the crank shaft side rotating body. By constraining of the relative rotation between both rotating bodies, even when the cam shaft undergoes positive and negative torque fluctuations due to a drive of the suction valve or exhaust valve, it is possible to prevent the generation of a hammering sound between the crank shaft side rotating body and the cam shaft side rotating body.
When changing the phase of the cam shaft side rotating body relative to the crank shaft side rotating body, the lock member is withdrawn from the housing by applying to the lock member an operating oil pressure that rotates the cam shaft side rotating body relative to the crank shaft side rotating body. As a result, relative rotation between the crank shaft side rotating body and the cam shaft side rotating body becomes possible.
Since the valve timing control apparatus which receives a drive force of the crank shaft by way of the timing gear or chain sprocket can be accommodated within an oil lubrication space of the engine, a back pressure chamber of the lock member opens to the oil lubrication space of the engine through a communication passage provided in the timing gear so that the lock member can be easily moved in its constraining position. Also, the operating oil discharged from the back pressure is returned to the oil lubrication space.
However, since the valve timing control apparatus receiving the drive force of the crank shaft by way of a timing pulley is disposed outside the oil lubrication space, the operating oil is discharged to outside the oil lubrication space when the operating oil in the back pressure chamber is discharged to outside the apparatus through a communication passage provided in the timing pulley. As a result, the operating oil decreases. Further, the operating oil discharged from the back pressure chamber is dispensed on a timing belt. As a result, the oil causes the timing belt to slip at its meshed portion between itself and the timing pulley and crank shaft. Further, the oil causes the timing belt to deteriorate.
Also, the back pressure chamber of the lock member remains open to the oil lubrication space regardless of the position of the relative rotation between the crank shaft side rotating body and the cam shaft side rotating body. Because the movement of the lock member is not regulated, there is the likelihood that the lock member will collide with other members to thereby generate undesirable hammering sounds.
Also, even when the crank shaft side rotating body and the cam shaft side rotating body rotate relative to one another, if the lock member is at all times in contact with an oil pressure chamber to supply the operating oil to the lock member in a direction of releasing the constraint, there is the likelihood that the lock member vibrates due to the pulsation of the operating oil supplied from an oil pressure source. As a result, the lock member collides with other members to thereby generate undesirable hammering sounds.